Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
2001-06-29
2004-09-07
Huff, Mark F. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
C430S311000, C430S396000
Reexamination Certificate
active
06787270
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to method for fabricating a liquid crystal display, and more particularly, to a photo mask for patterning a lightning rod which can be protected from static electricity.
2. Background of the Related Art
The liquid crystal display is provided with a liquid crystal panel having liquid crystal injected between upper and lower glass substrates, polarizing plates on both sides of the liquid crystal panel each for polarizing a light, a light source for providing a fixed back light to the liquid crystal panel, and a light plate, for displaying a video signal. The lower glass substrate of the liquid crystal panel is provided with a plurality of gate lines arranged in one direction at fixed intervals, data lines arranged in another direction perpendicular to the direction of the gate line at fixed intervals to define pixel regions, a matrix of pixel regions each formed between the gate lines and the data lines, a pixel electrode formed in each of the pixel regions, a plurality of thin film transistors each formed in a corresponding pixel region having a gate electrode connected to the gate line, a source electrode connected to the data line, and a drain electrode connected to the pixel electrode, for being turned on/off in response to a signal on the gate line, to provide a signal on the data line to the pixel electrode. The upper glass substrate is provided with a color filter layer, and black matrix or a common electrode. The foregoing upper and lower glass substrates are bonded together with a gap, and the liquid crystal is injected between the upper and lower glass substrates. There are pads at the ends of the data lines and the gate lines formed on the lower substrate, a shorting bar with a gap between it and the pads, and lightning rods between the shorting bar and the pads for protecting the thin film transistors from suffering damage caused by static electricity generated and flowing to the thin film transistor through the pad and the lines during a fabrication process. Each lightning rod has an outer lightning rod portion connected to the shorting bar, and an inner lightning rod portion connected to an inner line (pad), arranged opposite to each other with a fixed distance between the two, for causing a spark between the outer and the inner lightning rods if static electricity higher than a certain level is generated, for discharging the static electricity.
The lightning rod is formed by exposure and development by using a photo mask, a structure and principle of which will be explained with reference to the attached drawings.
FIG. 1
illustrates a plan view of a related art photo mask for patterning a lightning rod,
FIG. 2
illustrates a plan view of an actual pattern of a normal lightning rod obtainable when exposure/development and etching are carried out by using a photo mask as shown in
FIG. 1
,
FIG. 3
illustrates a plan view of a lightning rod when a pad is short circuited, which is a problem of the related art photo mask for patterning the lightning rod, and
FIG. 4
illustrates a plan view of a lightning rod showing another problem of the related art photo mask for patterning a lightning rod.
The related art photo mask for patterning a lightning rod with a shorting bar pattern
1
and pad patterns
4
is provided with an outer lightning rod pattern
2
connected to the shorting bar pattern
1
, and an inner lightning rod pattern
3
connected to the pads. The reference numeral
5
in
FIG. 1
denotes the lightning rod pattern, having the outer lightning rod pattern
2
and the inner lightning rod pattern
3
, arranged oppositely, each with a projection connected to the other with a fine pattern
6
for preventing static electricity in the photo mask. The fine pattern is extended from an edge of one of the projections in a diagonal direction to an edge of the other one of the projections. That is, one side of a portion of the fine pattern
6
connected to the projection forms a straight line and the other side forms a right angle. The fine pattern
6
is formed thus, for discharging static electricity generated at a cell array part of the photo mask toward an outer periphery of the mask through the fine pattern
6
and the shorting bar
1
, or draining the static electricity to ground, or neutralizing the static electricity by means of an ion generator, because the static electricity may cause a spark at the lightning rod pattern
5
of the photo mask, causing the lightning pattern
5
to suffer from damage, that may cause an unwanted pattern to be formed later in fabrication of the liquid crystal display.
A method for fabricating the lightning rod in a liquid crystal display by using the foregoing photo mask will be explained.
A conduction film is deposited on a glass substrate by photolithography for forming a gate electrode, a photoresist film is deposited on the conduction film, and a photo mask as shown in
FIG. 1
is used for patterning a shorting bar, pads, and a lightning rod by exposure, development, and etching. As shown in
FIG. 2
, if the patterning is done properly, the fine pattern
6
part of the photo mask forms no pattern on the glass substrate owing to interference and diffraction of lights in the exposure. That is, though the fine pattern connects the outer and inner lightning rods electrically on the photo mask, since the fine pattern has a very fine width, the fine pattern is not formed on an actually patterned lightning rod in a liquid crystal panel. Because the static electricity is required to be discharged, if the static electricity generated at the pads during a cell array fabrication process has a level great enough to break the thin film transistor in the cell, and because the lightning rod is required to be isolated from a driving voltage electrically, the gap between the lightening rod portions, and the shapes of the lightning rod portions, are required to be formed to correspond to a threshold value of the static electricity that is required to be discharged. That is, the smaller the gap of the lightning rods, and the sharper the lightning rods, the lower the voltage at which the spark occurs. Therefore, the gap between, and the shapes of, the lightning rods are required to be set up in designing the photo mask, and actually formed the same as the design. Accordingly, when the cell array of the liquid crystal display is formed properly actually as shown in
FIG. 2
, if the static electricity occurs at the pad during a cell array fabrication process, a spark occurs at the lightning rod, discharging the static electricity, and protecting the thin film transistor.
However, the foregoing related art photo mask for patterning a lightning rod in a liquid crystal display has the following problems.
First, since the very fine pattern formed between the lightning rod portions of the photo mask is susceptible to breakage such that the protection against static electricity for the photo mask can not be made, causing a spark between the lightning rod portions in the photo mask and damaging the photo mask resulting in a change in the gap or the shapes of the lightning rod portions, there may be cases when the static electricity generated at the cell array can not be prevented during fabrication of the liquid crystal display.
Second, despite the fact that the fine pattern is not intended to be formed between the lightning rods in fabrication of the liquid crystal display, there is a possibility that a fine pattern (dashed line) actually is formed between the lightning rods of cells in the liquid crystal display due to imperfect development and etching as shown in
FIG. 3
, causing a short with an adjacent pad, which causes trouble during electrical inspection of the cell array.
Third, though the lightning rods are required to have a fixed gap, a deformation at the part of the fine pattern acts as another lightning rod that changes the threshold voltage of the designed lightning rods.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a photo
Kim Yong Wan
Kwak Dong Yeung
Lee Seong Su
Yoo Soon Sung
Huff Mark F.
LG.Philips LCD Co. , Ltd.
McKenna Long & Aldridge LLP
Mohamedulla Saleha
LandOfFree
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